This type of escapement is known and disclosed in EP Patent No. B-18796 bearing the name of George Daniels as inventor. This escapement has several embodiments, the escape wheel set being able to be formed of a single wheel or two coaxially mounted wheels secured to each other. However, in this document, the gear train drives the wheel set via an escape pinion mounted in a conventional manner on the arbour of said wheel set and not directly via one of the wheels forming the wheel set.
In order to simplify the proposed system and especially to gain space heightwise, George Daniels developed a construction that he calls an ultra flat coaxial escapement and which he describes at pages 249 to 252 of his work “La Montre: principes et méthodes de fabrication”, Scriptar Editions S.A., La Conversion, Lausanne 1993. This construction includes a wheel set formed of two coaxial escape wheels secured to each other. The first wheel cooperates with two locking pallet stones and one impulse pallet stone arranged on the balance roller applying direct impulses thereto. The second wheel cooperates with an impulse pallet stone arranged on the pallet assembly, which applies indirect impulses to the roller. This second wheel is directly driven by the teeth with which it is provided, via the last wheel set forming the gear train of the timepiece. Thus the usual aforecited escape pinion is not used here, which contributes to reducing the thickness of the escapement system. Thus, an escape wheel set is assigned the dual function of receiving the movement from the gear train and contributing to at least one of the escapement functions. With George Daniels, there is only an indirect impulse function and it is clear that any other function assigned to the wheel set, except that cited, constitutes a novelty in the field of this type of escapement.
It will also be clear that the space requirement of the escapement heightwise can be still further reduced if it has only one wheel, the latter being directly driven by the gear train.